Cathode ray tube electron gun mount with unitary magnetic centering and gettering means



Aprli 25, 1967 B. J. SMITH 3,316,432

CATHODE RAY TUBE ELECTRON GUN MOUNT WITH UNITARY MAGNETIC CENTERING AND GETTERING MEANS Filed Nov. 13, 1963 2 Sheets-$heet l VERTICAL DEFLECTION SIGNAL SOURCE HORlZONTAL DEFLECTION yawm \ ivkaaqazfi 3 VERTICAL v43 DEFLECTION SIGNAL SOURCE INVENTOR BERNARD J. SMITH,

HIS ATTORNEY.

April 25, 1967 s rr 3,316,432

CATHODE RAY TUBE ELECTRON GUN MOUNT WITH UNITARY MAGNETIC CENTERING AND GETTERING MEANS Filed Nov. 13, 1963 2 Sheets-Sheet P,

INVENTORI BERNARD J. SMITH,

HIS ATTORNEY.

United States Patent C) a CATHODE RAY TUBE ELECTRON GUN MOUNT WITH UNITARY MAGNETIC CENTERING AND GETTERING MEANS Bernard J. Smith, Camilius, N.Y., assignor to General Electric Company, a corporation of New York Filed Nov. 13, 1963, Ser. No. 323,348 2 Claims. (Cl. 313-75) The present invention relates to improvements in electron beam centering devices for cathode ray tubes and particularly to static magnetic beam centering devices for cathode ray tubes, including kinescopes, iconoscopes, vidicons, and the like, having direct drive systems.

In cathode ray tubes designed for electromagnetic deflection of the electron beam, it is desirable to provide a beam centering means for centering the beam on the target or screen of the tube. In home television receivers, the electron beam is deflected in a series of vertically displaced horizontal scans to provide a rectangular scan raster on the display screen of the cathode ray tube. Ordinarily, centering of the beam and the scan raster is effected by proper orienting of a suitably energized deflection system and the tube. By electron-beam optics, there may be calculated a desired beam deflection center situated within the neck portion of the cathode ray tube from which the electron beam must be deflected for proper centering of the beam, and of the scan raster of the beam on the display screen. In electromagnetic deflection systems, an electromagnetic deflection yoke is positioned concentrically about the neck portion of the tube :at an axial displacement therealong which effects coincidence of the magnetic beam deflection center, defined by the windings of the yoke, and the desired beam deflection center. Generally, to effect this coincidence relationship, the yoke is positioned closely adjacent the flared-out portion of the tube which integrally joins the neck and screen portions. This positioning must be relatively exact if distortion-free images are to be produced on the screen of the display tube and properly centered thereon.

In the past, the electrical drive systems employed for energizing the electromagnetic deflection yokes to effect the scanning deflection of the electron beam usually. included an impedance coupling transformer for coupling the output signal from a deflection signal amplifier to the windings of the yoke. In these prior art systems, the use of the transformer for impedance coupling was necessary due to the relatively low impedance of the deflection windings of the yoke compared to the relatively high impedance of the vacuum tube in the output of the amplifier. Recent developments, however, have enabled the elimination of the coupling transformer. There are now available high impedance toroidally wound deflection yokes which may be directly driven by the output stage of the signal deflection amplifier. Conversely, transistorized amplifiers may be employed, the output impedance of which permits direct coupling to the more conventional, low-impedance magnetic deflection yokes.

The elimination of the coupling transformer is desirable in that it reduces manufacturing costs while contributing to a more eflicient system. Further, there is provided lighter weight, space-saving construction offering particular advantages in portable television receivers. Despite the many advantages gained by eliminating the impedancecoupling transformer, however, a very detrimental effect arises in direct drive systems due to the direct current 33%,432 Patented Apr. 25, 1967 7 coupling transformer, is directly coupled to the deflection windings in a direct drive system, producing a static magnetic field in the region of the desired beam deflection center. This static magnetic field effects a constant displacement of the magnetic deflection center from the desired deflection center, resulting in a constant deflection of the electron beam and consequent ofl-centering of the scan raster on the display screen. This off-centering effect i difficult to overcome by compensation in the deflection signal amplifier due to the complexities of the deflection field required to be generated by the windings of the yoke. Magnetic deflection compensation is diflicult to achieve due to the increasing compactness in design of cathode ray tube systems and due to the fact that attempted compensation by a magnetic field created externally of, and passing through, the field of the electromagnetic deflection yoke would require the compensating magnetic field to be of undesirably high strength, resulting in distortions in the scan raster.

It is therefore an object of this invention to provide an improved beam centering device providing centering of the electron beam in a cathode ray tube having electromagnetic beam deflection.

It is further an object of this invention to provide a beam centering device for use with a cathode ray tube having a direct drive electromagnetic deflection system.

It is still another object of this invention to provide a static magnetic beam centering device providing compensation for off-centering of the electron beam of a cathode ray tube having a direct drive electromagnetic deflection system.

connection between the output of the deflection signal I In carrying out this invention in one form thereof, there is provided a ring member mounted axially within the neck portion of a cathode ray tube, the ring member having a central aperture therein through which the electron beam passes. The ring member comprises structurally interconnected static magnetic beam deflection means and gettering means, the static magnetic beam deflection means producing a static magnetic field of parallel flux lines passing through the central aperture in a direction transverse to the electron beam in the region of a desired beam deflection center within the neck protion. An electromagnetic deflection yoke, the windings of which define a magnetic deflection center, is positioned concentrically about the neck portion of the tube and located thereon to eifect coincidence of the magnetic deflection center with the desired deflection center. The static magnetic field produced by the static magnetic beam deflection means compensates for off-centering of the electron beam effected by direct current energization of the windings of the deflection yoke in a direct drive system.

For a better understanding of the invention, a well as for further objects and features of advantage thereof, reference may be had to the following detailed description and drawings in which:

FIGURE 1 is a drawing of a cathode ray tube employing the device of the invention and including in schematic form a transistor-type electromagnetic direct drive deflection system,

FIGURE 2 is an enlarged view of the device of the invention taken along the section line 2-2 of FIGURE 1,

FIGURE 3 is a view of the device of the invention taken along the section line 3-3 of FIGURE 2,

FIGURE 4 is an alternative embodiment of the device of the invention,

FIGURE is a side view taken along the section 5-5 of FIGURE 4,

FIGURE 6 is a further alternative embodiment of the device of the invention, andv FIGURE 7 is a side view taken fromalong the line 77 of FIGURE 6.

In FIGURE 1 there is shown a cathode ray tube 10 having a neck portion 12 integrally joined with a screen (not shown) by flared-out portion 14.. Suitably mounted within the neck portion 12 is a cathode 16 arranged to be heated by heater 18 for the emission of electrons.

Various grid and accelerating electrodes 20, 22, 24, -26

and 28 are provided for forming the electrons into a beam and accelerating the beam along the axis XX through the neck portion 12.. For this purpose, suitablei electrical leads are indicated attached to the various electrodes, the lead 25 electrically interconnecting the accelerator electrodes 24 and 26 and electrical leads extending out the base (broken away) of the neck portion 12 and providing electrical connection to the grid electrodes 20 and 22 and the suppressor grid electrodev 28. V

Axially extending insulating arms 30, only one of which is seen in FIGURE 1, are joined peripherally to the" generally cylindrical electrodes 20, 22, 24, 26 and 28,mechanically interconnecting theseelements. The electrode 20 is secured to the base of the neck portion 12 and the electrode 26 is secured resiliently within the neck portion 12 by spacer members 32 and resilient spring members 34, wherebyall of the electrodes are axially mounted within the neck portion 12. In addition to providing structural support, the spacer members 32 and resilient spring'members 34 electrically connect the accelerator electrode .26 to thepcoating 36 conventionally employed incathode ray tubes as a sinkfor secondary electrons and as a post-deflection acceleration anode. The coating'36extends along the interior surface ofthe flared-out portion 14 of the tube 10' and connect-sthe accelerator-electrode 26 to the high voltage accelerating potential terminal 37; which extends through the wall of the flared-out portion 14 in a hermetically sealed fashion.

In operation, upon the application of suitable electrical which the electron beam must be deflected from its axial path for proper scanning .of the screen of thetube 10. I

Electromagnetic deflectionyoke 40 is positioned, concentrically about the neck portion 12 and firmly secured theretoj Although in the cross sectionof FIGURE 1 only I horizontal. deflection windings normally would be visible, the magnetic deflection yoke 40 has been indicated to inelude. both vertical deflection windings 42 and horizontal deflection windings 43. The vertical-deflection windings 42 .and ,the horizontal deflection windings 43 define a I magnetic deflection center at which the electron beam is "deflectedto'effect the scanning; Ideally, the magnetic deflection center will coincide with'the desired 'beamdcfleet-ion center at the point 38.

Referring to FIGURE 2, a cross sectional view ofthe neck portion 12 and the coating 36 is shown; The electro-- ma-gneticdeflection yoke 40 is generally indicated in dottedv lines surrounding the neck portion '12, of the tube 10, the windings of the yoke 40 being schematically represent-' ed by the series-connected vertical deflection windings 42 and the horizontal magnetic deflection windings 43.

. A vertical beam deflection circuit 44 for IhCKGlfiCtl'O.

magnetic deflection yoke 40 is indicated in schematic form "in FIGURE 1, and comprises a vertical deflection signal source 46 connected to the base 48 of transistor 50, the

base 48 also .being connected through resistor 52 to -The-emitter 54 is connected to a source of for-- ward biasing potential 56, and the collector 58 is connected to one terminalof the vertical deflection windings 42 of the electromagnetic deflection yoke 40, the other terminal of the vertical deflection windings 42 being connected through a suitable source of collector biasing potential 60 to ground. The deflection circuit 44 energizes the vertical deflection windings 42. of the electromagnetic deflection yoke 4t). which in turn produce a field of magnetic flux passing transverse to the path of the electron beam and effecting vertical deflection of the electron beamfor scanning the display screen.

The circuit 44 comprises a direct drive system, evidenced by the direct connection of the collector 58 to the vertical deflection windings 42. Even in the absence of a deflection signal from the deflect-ion signal source 46, there exists a residual collector-emitter current from the potential sources 56 and 60. Due to the direct connection, the residual current passes through the vertical deflection windings 42 of the yoke 40, creating electromagnetically a static flux field in the vicinity of the desired beam deflectioncenter. The static electromagnetic flux will displace the ma-gnetic deflection center from the axial location 38 of the desired beam deflection center. Thus, the electron beam will be deflected, in scanning the screen, from a deflection center which is vertically displaced from the location 38 of the desired beam deflection center, and the raster scan will be off-centered on the display screen.

In accordance with this invention, the decentering eflfeet of the direct drive deflection system is compensated by the addition of a static magnetic deflection means structurally interconnected with a gettering means and POSI', tioned axially within the neck portion of the tube. The static magnetic deflection means creates a static magnetic field of parallel flux lines passing in a transverse direct-ion to the electron beam in the regionof the desired deflection center at 38 which compensates for the off-centering of the beam arising from the static field generated by the direct drive system.

The structurally interconnected member comprising both the gettering means and the static magnetic deflection means is indicated generally by the annular member 62 which is mounted axially within the neck portion 12 by straps 64. Referring to FIGURE 2, the structurally interconnected static magnetic'deflection means and gettering passes.

means is seen, in general outline, to be ring-shaped there by providing a central circular aperture port-ion 65 through which a planar field of horizontal parallel flux lines 63 plane such as to compensate for the vertical displacement of the magnetic beam deflection center from the desired beam de'flection'center 38 due to the direct or static current component of the energizing current in the vertical deflection windings 42 of the magnetic deflection yoke 40 in a direct drive system. Thus, the resultant magnetic beam mounted symmetrically thereon, the annular member 62- supporting the members 68 and 69 for concentric positiondeflection center is made to coincide with the desired beam deflection center to provide proper centering of the electron beam.

It is noteworthy that the annular member 62 is a combined gettering means and static magneticbeam deflection means.

'frequently positioned in the immediate vicinity of the desiredbeam deflection center such as at 38. Thus, in the embodiment of the invention shown in FIGURES 2 and 3, the annular member 62 may comprise a gettering ring 66 component ofthe energizing current in the vertical deflechaving arcuate permanent magnet members 68 and 69 ing within the neck portion 12. The gettering ring 66 has a channel or recess 70 within which gettering material 72 is received for structural support thereof during assembly The flux lines 63 are directed in the horizontal;

of the tube. The arcuate magnets 60 and 69 are mounted on the solid planar wall 67 of the gettering ring 66 in any suitable fashion, such as by welding.

In FIGURES 4 and 5 there is shown an alternative embodiment of the invention comprising a gettering ring 66 similar to that of FIGURES 2 and 3, and having a recess 70 therein within which gettering material 72 is received. Mounted on the planar wall surface 67 thereof is an annular magnet 74 which is polarized at diametrically opposed ends thereof to create a field of parallel magnetic flux lines 63 in the same manner as indicated in FIG- URE 2.

In a further embodiment of the invention, shown in FIGURES 6 and 7, a permanent magnet is employed which, in addition to providing a static magnetic field, also provides the structural support of the gettering material. In FIGURE 6, a permanent magnet 76 of an annular shape is provided with a central aperture 65 through which the field of parallel magnetic flux lines 63 passes. The crosssectional view of FIGURE 7 indicates that the annular magnet 76 is provided with an annular recessed portion 78 Within which gettering material 72 is received.

The various embodiment-s of the invention shown and described herein are effectively functional equivalents of one another and each may be positioned within the neck 12 of the tube as is indicated by the annular member 62 in FIGURE 1 for creating the static magnetic field of parallel flux lines required for centering of the electron beam.

In the system shown, compensation has been provided for only vertical deflection or off-centering of the beam, it having been assumed that the beam is properly centered in the horizontal plane. It is apparent, however, that horizontal off-centering of the electron beam may be compensated by a static magnetic deflection means in accordance with the invention when mounted at a suitable angular orientation within the neck portion 12.

The usefulness of the device of the instant invention will be readily appreciated by those skilled in the art. The use of a ring-shaped or annular gettering member positioned axially within the neck of the tube and adjacent the desired beam deflection center is rather standard construction, especially in short-necked cathode ray tubes. Thus, the device of the invention encompasses the use of a structure conventionally employed, namely, the getterin-g means, and combines with it the static magnetic deflection means which, because of its strategic positioning within the neck of the tube, and because of its structural interrelation with the gettering means, provides an extremely effective beam centering device. Further, the simplicity of the structure and the relative ease in mounting of the beam contering device of the invention provide a structure which is very inexpensive to manufacture It will be obvious to those skilled in the art that many variations and modifications of the beam centering device of the invention may be made without departing from the spirit and scope of the invention. Therefore, this invention is to be considered as limited only in ac cordance with the teaching thereof as set forth in the claims appended hereto.

What I claim as new and desire to be secured by Letters Patent of the United States is:

I. In a cathode ray tube having integrally joined neck and screen portions wherein an electromagnetic deflection yoke is axially mounted on the neck portion and energized for deflecting an electron beam passing therethrough for scanning the screen portion of the cathode ray tube, and wherein the magnetic beam deflection center defined by the yoke is to coincide with a desired beam deflection center within the neck portion, a beam centering device comprising an annular permanent magnet mounted axially Within the neck portion of the tube and providing a central aperture through which the electron beam passes, said annular permanent magnet having a recess therein for reception of gettering material, and being poled to produce a static magnetic field of parallel flux lines extending across said aperture in a direction transverse to the electron beam in the region of said desired beam deflection center for effecting a constant deflection thereof sutficient to center the electron beam on the screen portion.

2. In a cathode ray tube having integrally joined neck and screen portions wherein an electromagnetic deflection yoke is axially mounted on the neck portion and energized for deflecting an electron beam passing therethrough for scanning the screen portion of the cathode ray tube, and wherein the magnetic beam deflection center defined by the yoke is to coincide with a desired beam deflection center Within the neck portion, a beam centering device comprising an accelerator electrode mounted adjacent said beam deflection center within the neck portion and an annular permanent magnet mounted on said accelerator electrode for concentric positioning thereof within the neck portion and having a central aperture through which the electron beam passes, said annular permanent magnet having a recess therein for receiving getterin g material and being poled to produce a static magnetic field of parallel flux lines extending across said aperture in a direction transverse to the electron beam in the re gion of said desired beam deflection center for effecting a constant magnetic deflection thereof sufficient to cen ter the electron beam on the screen portion,

References Cited by the Examiner UNITED STATES PATENTS 6/1957 Finkelstein et al 31376'.

5/1965 Benway 313-181 

1. IN A CATHODE RAY TUBE HAVING INTEGRALLY JOINED NECK AND SCREEN PORTIONS WHEREIN AN ELECTROMAGNETIC DEFLECTION YOKE IS AXIALLY MOUNTED ON THE NECK PORTION AND ENERGIZED FOR DEFLECTING AN ELECTRON BEAM PASSING THERETHROUGH FOR SCANNING THE SCREEN PORTION OF THE CATHODE RAY TUBE, AND WHEREIN THE MAGNETIC BEAM DEFLECTION CENTER DEFINED BY THE YOKE IS TO COINCIDE WITH A DESIRED BEAM DEFLECTION CENTER WITHIN THE NECK PORTION, A BEAM CENTERING DEVICE COMPRISING AN ANNULAR PERMANENT MAGNET MOUNTED AXIALLY WITHIN THE NECK PORTION, A BEAM CENTERPROVIDING A CENTRAL APERTURE THROUGH WHICH THE ELECTRON BEAM PASSES, SAID ANNULAR PERMANENT MAGNET HAVING A RECESS THEREIN FOR RECEPTION OF GETTERING MATERIAL, AND BEING POLED TO PRODUCE A STATIS MAGNETIC FIELD OF PARALLEL FLUX LINES EXTENDING ACROSS SAID APERTURE IN A DIRECTION TRANSVERSE TO THE ELECTROM BEAM IN THE REGION OF SAID DESIRED BEAM DEFLECTION CENTER FOR EFFECTING A CONSTANT DEFLECTION THEREOF SUFFICIENT TO CENTER THE ELECTRON BEAM ON THE SCREEN PORTION. 